The present invention relates to a method for determining the switching pressure of a safety appliance which is adapted to safeguard an installation against exceeding or falling below a gas pressure, wherein an increasing pressure is applied to the safety appliance.
Such a method is generally known. It is used to measure the switching pressure of safety appliances in order to check whether a safety appliance is functioning correctly and to check whether a safety appliance is functioning at the correct pressure.
It is of course of the greatest importance that such safety appliances respond at this correct gas pressure.
According to the prior art use is made herein of a method wherein a pressure is supplied to the safety appliance and this pressure is gradually increased until the safety appliance responds. The pressure at which this takes place is recorded, whereafter it can be compared with the nominal operating pressure and the functioning of the appliance can thus be determined.
Experience shows that the operation of such a safety appliance is usually dependent not only on the supplied pressure but also on the degree of change in the gas pressure, or in other words the derived function of the function representing the gas pressure in time. This is found to be particularly the case in situations where such safety appliances have not functioned for a long period, as will fortunately usually be the case.
This means that the safety measurements are therefore dependent upon more than one variable, so that the measurement is normally difficult to reproduce.
The object of the present invention is to provide a method and an apparatus with which the above stated drawbacks of the prior art can be avoided.
This object is achieved by a method for determining the switching pressure of a safety appliance which is adapted to safeguard an installation against exceeding or falling below a gas pressure, wherein an increasing pressure is applied to the safety appliance, which method is characterized in that the supplied increasing pressure rises in accordance with an exponential function.
Owing to the constant relative increase in the pressure supplied to the safety appliance, it is no longer necessary beforehand to take into account settings of the safety appliance. Errors resulting from incorrect settings by the user are hereby prevented.
The present invention further provides a measuring device for generating a gas pressure increasing in time, which is characterized in that the measuring device is adapted to generate a gas pressure rising in accordance with an exponential function.
According to a particular preferred embodiment the supplied pressure is blown off after reaching a maximum permissible pressure which exceeds the switching pressure of the safety appliance.
It will be apparent that this measure will greatly increase the safety of the person performing the method in question.
According to another preferred embodiment the measuring device comprises a vessel with a constant volume and a supply element which is adapted to supply a gas flow to the vessel, the flow rate of which is proportional to the pressure in the vessel.
This is found to be a particularly attractive method of building up a gas pressure rising in time in accordance with an exponential function.
According to another preferred embodiment the supply element is formed by a laminar element which is arranged in a gas conduit and which is connected on one side to the vessel and connected on the other side to a pressure source, the pressure of which is always a factor higher than the pressure in the vessel.
According to yet another preferred embodiment the measuring device comprises a pressure amplifier, the inlet connection of which is connected to the vessel and the outlet connection of which is connected to the other side of the laminar element.
Other attractive preferred embodiments are specified in the remaining sub-claims.